A method of detecting a ferroelectric signal from a ferroelectric film and a piezoelectric force microscopy (PFM) apparatus are provided. The method includes following steps. An input waveform signal is applied to the ferroelectric film. An atomic force microscope probe scans over a surface of the ferroelectric film to measure a surface topography of the ferroelectric film. A deflection of the atomic force microscope probe is detected when the input waveform signal is applied to the ferroelectric film to generate a deflection signal. Spectrum data of the ferroelectric film based on the deflection signal is generated. The spectrum data of the ferroelectric film is analyzed to determine whether the spectrum data of the ferroelectric film is a ferroelectric signal or a non-ferroelectric signal.